Polylactic acid is one kind of biodegradable polymer, and can be produced using reproducible plant resources, food residuals from everyday life, old papers or the like and without using petroleum resources. Further, since the waste thereof is degraded in nature, it is less likely that the disposal of the waste becomes a problem as with conventional plastic products. Therefore, polylactic acid is expected to play a large role in solving problems of resources, energy and environment from the present to the future.
Specifically, in the case that polylactic acid is used for agricultural materials or the like, it is not necessary to collect them after use. Further, in case that polylactic acid is used in a packing container of a packed lunch at a convenience store or food, the container can be disposed as garbage without separating leftovers or food after use. Therefore, since polylactic acid allows the rationalization of a material cycle or transportation by utilizing characteristics of a biodegradable resin originated in plants, polylactic acid can contribute largely to saving labor and saving energy. Further, also in the case of using polylactic acid in living bodies, since its degradation products are lactic acid, carbon dioxide and water, which are harmless to a human body, polylactic acid can be used as a medical material or the like.
However, while polylactic acid is excellent in transparency as PS resin and PET resin, there is a problem of being inferior in heat resistance, moldability and mechanical strength such as impact property. Such properties have been a problem on attempting to expand a broad range of use.
In order to improve the heat resistance, moldability and mechanical strength such as impact property of polylactic acid, a method is attempted, in which fillers such as silica is blended with polylactic acid. Such a technique is described in Japanese publication of patent application Nos. 2005-200600, 2005-112456 and 2004-224990.